The present invention generally relates to telecommunication apparatuses and more particularly to a large-capacity optical telecommunication apparatus carrying out multiplexing and demultiplexing of optical signals.
In the field of telecommunication, the information content or amount of information to be handled by a telecommunication apparatus is increasing sharply in relation to the increasing need of transmitting audio and/or visual data. In correspondence to such an increasing need of transmitting large amount of information, the telecommunication apparatuses used in a telecommunication station for handling a telecommunication traffic is now going to be updated, from a conventional apparatus that converts optical signals once into electrical signals for conducting the signal multiplexing, to a new type apparatus in which the optical signals are multiplexed directly. In order that such a new, full-optical telecommunication apparatus is used extensively in telecommunication stations, it is necessary to design the full-optical telecommunication apparatus for easy maintenance and such that increase or decrease of optical cables, and the like, is achieved easily without exposing the optical cables to the risk of being damaged.
FIGS. 1A and 1B show the process of adding an optical cable in a full-optical telecommunication apparatus that carries out a full-optical signal multiplexing, wherein FIG. 1A shows the state before the addition of the optical cable while FIG. 1B shows the state after the addition of the optical cable.
Referring to FIG. 1A, it can be seen that there is provided an optical signal multiplexing module 10 to which two optical cables, 11.sub.--1 and 11.sub.--2 are connected. The optical signal multiplexing module 10 is connected to a power supply 12 and carries out a multiplexing of the optical signals transmitted through the optical cables 11.sub.--1 and 11.sub.--2. As a result of the multiplexing, the optical signal multiplexing module produces a multiplexed optical signal. The multiplexed optical signal thus produced is supplied to an output optical cable 13.
FIG. 1B shows the case in which another optical cable 11.sub.--3 is added for dealing with the demand of increasing the information content handled by the optical signal multiplexing module 10.
Referring to FIG. 1B, the optical cable 11.sub.--3 is newly connected to the optical signal multiplexing module 10, and the optical signal multiplexing module 10 carries out a multiplexing of the optical signals in the optical cable 11.sub.--3 with the optical signals in the optical cables 11.sub.--1 and 11.sub.--2. The output optical signal thus produced as a result of the multiplexing is supplied to the optical cable 11.sub.--3.
In the process of connecting the optical cable 11.sub.--3 to the optical signal multiplexing module 10, it is important to maintain the connection of the optical signal multiplexing module 10 to the power supply 12. Otherwise, the optical signal multiplexing module 10 is momentarily shut down and the optical transmission via the optical signal multiplexing module 10 is interrupted. In order to avoid such an interruption of the optical transmission, it is desired to construct the optical signal multiplexing module 10 such that the connection of additional optical cables is possible while powering the optical signal multiplexing module 10 by the power supply 12.
FIG. 2 shows the construction of a conventional optical telecommunication apparatus 29 disclosed in the Japanese Laid-Open Patent Publication 8-204358.
Referring to FIG. 2, the optical telecommunication apparatus 20 includes a shelf 22 accommodating therein a plurality of substrate modules 22 in a state that the substrate modules 22 are inserted in the X.sub.1 -direction and held parallel with each other. Each of the substrate modules 22, in turn, has a construction in which a main substrate 23 supports thereon a sub-substrate 24. The sub-substrate 24 is formed with plurality of elongated holes 24a and is held slidably on the main substrate 23 in the X.sub.2 -direction by engaging the elongated holes 24a with corresponding pins 23a that are provided on the main substrate 23. It should be noted that main substrate 23 carries electronic components, while the sub-substrate 24 carries an optical connector 25. Further, the main substrate 23 is connected to a back board (not shown) provided inside the shelf 21.
In the optical telecommunication apparatus 20, the optical telecommunication apparatus 20 is connected to an external optical cable 27 in the state that the sub-substrate 24 is pulled out from the shelf 21 in the X.sub.2 -direction. During such a process of connecting the optical cable 27, the electrical connection between the main substrate 23 and the back board is maintained.
In the optical telecommunication apparatus 20 of FIG. 2, it should be noted that the process of pulling out the sub-substrate 24 from the shelf 21 in the X.sub.2 -direction tends to cause a damage in the optical cables 27 that are already connected to the sub-substrate 24 as the optical cables 27 are pulled in the X.sub.2 -direction together with the sub-substrate 24. Further, such a process of pulling the sub-substrate 24 in the X.sub.2 -direction tends to become difficult due to the resistance of the optical cables 27. This problem becomes particularly serious when there are a number of optical cables 27 already connected to the sub-substrate 24.
In addition, the prior art construction of FIG. 2 has a drawback in that the pins 23a provided on the main substrate 23 reduces the effective area of the main substrate 23 for carrying the electronic components.